Mobility management generated - Charging Data Record

Description

The Mobility management generated - Charging Data Record (M-CDR) is a standardized data structure defined across multiple 3GPP specifications, including TS 32.251, 32.272, 32.273, and 32.278. It is a subtype of Charging Data Record (CDR) specifically created by core network nodes responsible for mobility management. In the Evolved Packet Core (EPC), the Mobility Management Entity (MME) generates M-CDRs, while in the 5G Core (5GC), the Access and Mobility Management Function (AMF) takes on this role.

An M-CDR works by logging discrete mobility management events as they occur during a subscriber's session. The charging function within the MME or AMF is triggered by specific signaling procedures. For each significant mobility event, it opens a new M-CDR or updates an existing one, populating it with a wealth of structured information. This includes the IMSI or SUPI of the subscriber, the event type (e.g., 'Attach', 'Tracking Area Update', 'Handover'), timestamps for the event's start and stop, the serving cell and tracking/routing area identifiers, and the peer network element involved (e.g., source and target eNodeB/gNodeB for a handover).

Key components in its generation are the Charging Trigger Function (CTF) embedded within the MME/AMF and the offline charging system (OFCS). The CTF detects chargeable events, assembles the relevant data into a CDR data unit, and forwards it via the Rf/Ga reference point to the Charging Data Function (CDF). The CDF then formats this into a final M-CDR file for the Billing Domain. The M-CDR's role is to provide a non-real-time, detailed log of 'control plane' mobility activities. It does not charge for user data volume but for network resource usage related to mobility processing. This record is essential for operators to understand subscriber movement patterns, perform roaming settlements, support lawfully authorized requests, and implement certain billing models that account for mobility (e.g., regional tariffs).

Purpose & Motivation

M-CDRs exist to fulfill the critical operational and commercial need to account for mobility management signaling as a chargeable network service. In early cellular networks, charging was primarily based on voice minutes or simple data volume. As networks evolved to packet-switched architectures with complex mobility support (handovers between cells, routing area updates, etc.), these signaling procedures consumed significant processing resources in the network core.

The problem was that this resource consumption was not captured by traditional S-CDRs (Session CDRs) or G-CDRs (Gateway CDRs), which focused on data session activity and traffic volume. Operators had no standardized way to track, log, and potentially bill for the costs associated with managing a highly mobile subscriber. The creation of the M-CDR in 3GPP Release 8 with the EPS addressed this gap. It was motivated by the requirement for granular, standardized charging data for all network services, enabling fairer cost allocation, detailed analytics on network load due to mobility, and accurate inter-operator roaming charges for mobility events. It provides the audit trail necessary for the business and operational support systems (BSS/OSS) in a modern, packet-based mobile network.